Polyfurcous fuel



Patented Jam", 1939 POLYFURCOUS FUEL Carleton Ellis, Montclair, N. 1.,assignmto Standard Oil Development Company, a corporation of Delaware NoDrawing.

10 Claims.

This invention relates to motor fuels for internal combustion enginesand particularly to automotive gasoline fuels adapted to igniteadequately at relatively low engine temperatures. it involves thetreatment of petroleum of the gasoline type and related fuels cheaply toconfer thereon the quality of lower ignition temperature and also theregulated and controlled. addition of polyfurcous ethers and esters tosuch fuels.

In an internal combustion engine, ignition of gasoline, or other motorfuel, takes place under a pressure considerably greater than atmosphericpressure, say 75 to 100 pounds per square inch. Under such pressures,the air or other oxygencontaining supporter of combustion apparentlyexerts a different degree of selectivity than at atmospheric pressure.

In the starting of cold engines, or when the engine is run at lowtemperatures, for example an all airplane motor at high altitudes,vaporization of the fuel under engine pressures may not take placesufficiently rapidly to allow smooth and sustained combustion of thefuel. These ignition difiiculties may be eliminated, or to a largedegree palliated and counteracted, by the utilization of selectivepriming compounds, includingthose of petroleum origin or self-made,which are intended to become extremely flammable or ignitible at enginepressures thereby resulting in the easy ignition of the compressedfuel-vapors. F ich selective priming compounds although confr ring upongasoline, or other motor fuels, anincreased ignitibility at enginepressures do notv necessarily render the fuel more ignitible atatmospheric pressure and, therefore, the fire-hazard connected with theuse and handling of a motor fuel of such increased ignitibility shouldnot be greater than that ordinarily encountered under similar conditionswith a normal motor fuel, e. g., gasoline.

One method whereby I obtain ignition temperature depressants is bytreating the fuel with a nitrating agent. Nitration may be carried outat room temperature, or at slightly higher temperatures. Nitration canbe effected by treating the motor fuel with higher oxides of nitrogen,in

which case the oxides in gaseous form are passed into the fuel which maybe mechanically agitated.

Oxides of nitrogen may be prepared, for example, by the action ofsulphuric acid on sodium or potassium nitrite, by the action of nitricacid on copper, by the passage of air (i. e., a gas containing bothoxygenv and nitrogen) through an electric arc, bythe catalytic oxidationof ammonia, or by any other convenient method. Preferably a smallproportion of air, or of otheroxygen-con- Application January 31, 1935,Serial No.4,301

taining gas, is mixed with the oxides of nitrogen before passing intothe fuel. In some instances dilute nitric acid is employed fornitration. For example, in some cases a fuel may be nitrated by warmingand thoroughly agitating 100 volumes thereof with volumes of nitric acidof specific gravity 1.05. After nitration, any acidic or corrosivecompounds present in the motor fuel may .be removed by washing thetreated fuel with water or. a dilute solution of caustic soda or otherwater-soluble alkali, orby any other appropriate means.

It is desirable in the nitrating operation that vigorous oxidation orother undesirable reactions resulting in the formation of sludge beavoided as far as possible. For this reason the proportion of nitratingagent and the temperature of nitration will vary with different fuels.

Substances included in the term nitro compounds are not only those inwhich a nitro, or N02, group is inflxed or implanted in the molecule,and which are often'produced by the action of nitric acid and sulphuricacid on parailinic or cyclic hydrocarbons, but also suchnitrogen-containing compounds as nitrosites and nitrosates. The formertype (nitrosites) are compounds formed by the interaction of nitrogentrioxide and olefins, while the latter (nitrosates) are the result ofthe reaction between olefins and nitrogen tetroxide. The olefins areeither acyclic or cyclic. In some instances nitric acid reacts directlywith certain types of unsaturated hydrocarbons forming addition productsof the nitro type. All such compounds, containing these variousnitrogenpxygen groupings, when present in the fuel, may .serve alone orwith addition of other selective primers to depress ignition temperaturesumciently.

In making motor fuel of improved ignitibihty it is preferable in manycasesto.treat only a portion of the fuel and then add this treatedportion to the main body of the fuel. For instance, ordinary gasoline isa mixture of various hydrocarbons whose boiling ranges extend from, say,60 to 400 F., or thereabouts. Such a fuel may be separated, for example,by distillation into two fractions boiling, say, between 60 and 175 F.and 175 and 400 F. The latter, or higher boiling, fraction may benitrated by any of the foregoing procedures, and then blended with thelower fraction to furnish a motor fuel of the proper boiling range.

Any light mineral oil distillate which can be used as a gasoline type ofmotor fuel may be nitrated and the distillate so treated employed in thepreparation of motor fuel. By the term mineral oil is meant petroleumoil, rockoil, shale-oil, and the like.

Another procedure whereby I may obtain a fuel of improved ignitibilityincludes the addition of oxygenated hydrocarbons, particularly thoseoxygenated hydrocarbons which contain polyfurcous structures. Suchcompoundsembrace acetals of secondary and tertiary alcohols, esters ofthese alcohols with alkyl substituted organic acids, and polyfurcousketones. An example of an acetal is diisopropyl formal made fromformaldehyde (or trioxymethylene) and isopropyl alcohol, of an ester isthe tertiary butyl ester of trimethylacetic acid, and of a ketone ispinacolin (or ter butylmethyl ketone) prepared from acetone. Substitutedacetals, such as acetone-diethyl-acetal,

, which is derived from acetone and ethyl alcohol,

may be employed also. Addition of such compounds, possibly because ofthe presence therein of one or more oxygen atoms per molecule, not onlyassists in increasing the ignitibility or flammability of the fuel underengine operating conditions, but also because of their polyfurcousstructures, which is associated with the property of antiknocking,maintain or improve the antidetonating qualities of the motor fuel.Thus, by incorporating one or more oxygenated hydrocarbons of the abovementioned types. with the fuel there results, on the one hand, anincrease in ignitibility of the fuel and, on the other hand, a decreasein its tendency to knock during combustion in the engine. Substanceswhich exhibit simultaneously these dual properties are designatedantiknock-igniters. I

As an oxygenated antiknock-igniter I prefer to use a compound whichcontains at least three carbon atoms in its molecular trunk or stem andwhich possesses bifurcous terminals. By stem or trunk is meant thoseatoms which may be-represented as joined together in a straight line.

Branching is considered as consisting of at least two radicals, e. g.,two methyl groups, attached to one carbon atom. n the other hand, aradical and an element (say, a methyl group and a hydrogen atom)attached to. a carbon atom is not considered as branching. Forexampla'diisopropyl formal CH: CH:

contains a trunk of five units, three carbonhydrogen and two oxygen(indicated by the dotted lines), and two bifurcous branches. Diisopropylacetal OH: CH:

branches, in order to secure a maximum degree of ignition-temperaturedepression, quick pickup, and knock reduction. Insofar as possible Idesire to make such antiknock-igniters from bydrocarbons present incrude petroleum or its distillates, or which are procured as by-productsfrom various refinery operations, such as distillation, cracking,hydrogenation, etc. To illustrate, the cracking gases obtained duringcracking of high-boiling petroleum distillates contain a substantialproportion of olefin hydrocarbons, e. g., ethylene, propylene, andbutylenes. A part of these gases can be submitted to pyrolytic treatmentunder suitable conditions, such as passage through the electric arc, tofurnish a good proportion of acetylene. Catalytic hydration of acetylenefurnishes acetaldehyde. Another part of theolefin-containing gas istreated with sulphuric acid to give alkyl sulphuric acid esters, whichon hydrolysis and distillation yield second ary and tertiary alcohols,e. g., isopropyl and tertiary butyl alcohols. Similarly, secondary andtertiary amyl and hexyl alcohols can be made from the low-boilingcondensate separated from cracking gases by compression and/orabsorption processes. Acetaldehyde can be condensed, for example, withsecondary butyl alcohol, in the presence of a catalyst, such as hydrogenchloride or phosphine, to give the antiknock-igniter,acetaldehyde-di-sec-butyl acetal,

C"; CH: CH: I GHQ ('10 CH CzTl's H C255 In addition to usingolefin-containing gases as the source of acetylene I may employ alsogases consisting substantially of saturated or paraffinic hydrocarbons.Such gases are obtained, for example, by the distillation of crudepetroleum or by the stabilization of gasoline or casing-head naphtha.These gaseous paraflin hydrocarbons when passed through an electric arcyield a substantial proportion of acetylene, which can be hydrated toacetaldehyde. The aldehyde can be condensed with alcohols made asdescribed above. In some instances hydration of acetylene may beomitted, and direct etherization to polyfurcous antiknock-igniters beeffected by passing acetylene into the alcohol, at somewhat elevatedtemperatures, in the presence of catalysts.

Secondary alcohols prepared from cracking gas, as described above, mayserve as the source of antiknock-igniters. For example, acetone isobtained by the catalytic oxidation of isopropyl alc'ohol and thisketone can be converted by suitable methods to the dihydroxy alcohol,pinacol. The latter in acid media undergoes molecular rearrangement(with the loss of water) to give the polyfurcous ter-butyl-methylketone,

Or when subjected to the action of alkalies, e. g., calcium oxide,acetone yields a branched-chain unsaturated ketone, mesityl oxide,

I 011: CH3

Furthermore, subjecting isopropyl alcohol to high temperatures (500-700C.) furnishes a composition (cracked isopropyl alcohol) containingacetone and unchanged alcohol, the major proportion of the compositionbeing acetone. Cracked isoproyl alcohol, with or without the addition ofdefinite proportions of antiknock-igniters, can be blended with gasolineto secure a motor fuel of increased ignitibllit-y. Alternatively crackedisopropyl alcohol may be subjected 'to the action of alkalies wherebythe acetone therein is converted, wholly or in part, to the anti-,

knock-igniter mesityl oxide and various proportions of thealkali-treated cracked isopropyl alcohol blended with gasoline. The useof condensation products of acetone with aldehydes, for exampleformaldehyde, is not precluded provided the addition of such products togasoline does not result in the motor fuel exhibiting objectionablefeatures.

Antiknock-igniters are particularly advantageous in the production ofracing fuels. With fuels of this type it is especially necessary thatthey be readily ignitible at low engine temperatures, possess highantiknock value, burn cleanly in order to eliminate as much as possiblecarbon 'sented by altitude changes.

formation and deposition in the engine and on the valves, and exhibit aquick pick-up. For these reasons the proportion of antiknock-igniter inracing fuels is much greater than in fuels intended for use in the usualtypes of internal combustion engines, preferably the proportion ofantiknock-igniter being as high as or per cent, or even higher.

Combinations of the foregoing procedures can be employed in making fuelsof improved ignitibility. For example, ordinary gasoline, as previouslymentioned, can be separated by distillation into two fractions, oneboiling between 60 and F., and the other between 175 and 400 F., and thehigher-boiling fraction subjected to a nitrating operation. To thelower-boiling fraction is added a minor proportion of anantiknockigniter. The two fractions are then blended to furnish a motorfuel of the proper boiling range. Or, a portion of the gasoline may benitrated, and an antiknock igniter added to the other portion. These twoportions can be blended in any desired proportions. In some instancesthe nitration step may result in a decrease in antiknock value of themotor fuel. Any decrease in antiknock value can be compensated to agreater or lesser degree by the direct addition of a suitable proportionof antiknock-igniter., In some instances an. increase in antiknockvalueof the composite fuel is obtained by employing a suffieiently largeproportion of the antiknock igniter. I regard the step of lowering thenormal temperature of ignition byincorporating substantially at the timeof use small proportions of a sub: stance, or of substances, capable ofcausing such lowering to be of advantage when, for example, as in thecase of an aviation engine, the air supplied to the engine forcombustion of the fuel is subjected to rapid changes in density duetomovement of the aircraft upwards into more and more rarified air ordownward from a high altitude into a denser atmosphere. In such casesthereis permitted a further adjustment of the fuel to fit changingconditions, namely, the addition of variable amounts of the ignitiontemperature depressant to the fuel, thus to activate combustion underthe immediate conditions pre- One way of accomplishing this regulationis the introduction of activating agents, such as various oxygenatedand/or nitro compounds, in requisite proportion, the activating agentpreferably being first dissolved in some of the motor fuel to make aconcentrate and the latter added slowly in gradual and regulated flow tothe fuel feed to the engine, there mixing with the main fuel feed supplyin the desired proportion to secure ignition 'temperature "resume-aaridffothr qualities that may be required with fluctuations in altitude.If desired the flow of the activating concentrate to the mixingchamberor zone may be adjusted automatically with'the' altitude byappropriate means. In this manner the proportion of antiknock-igniter orother catalyst of temperature-lowering ignition admitted to thecombustion chamber is altered in accordancewith pressure fluctuation dueto rapid variation in atmospheric pressure. It should be noted that thisproportion, roughly speaking, may be regarded as an inverse ratio, thatis. the lower the atmospheric density the greater theproport'ion ofcatalyst oftemperature-loweringignition ad-' the ignition-temperaturedepressants employed in i the motor fuel. Adding small proportions ofsoaps or thickeners, of which cobalt naphthenate or cobalt slats ofacids made by oxidation of par-- allin wax, ozokerite, Montan wax, andthe like. are examples, increase the viscosity of the fuel to a veryslight degree. This increase in viscosity, although almost imperceptibleto the eye, is suificient to decrease the flow of fuel through thecarburetting device slightly, thereby resulting in somewhat less fuelconsumption without decreasing the efficiency of the engine. smallproportion of highly refined lubricating 'or solvent oils, which have novalue as volatile motor fuels, serves to prevent or remove gum depositson such portions of the engine as the intake manifold or the valves.Oil-soluble dyes, of any desired color, can be employed to distinguishthe fuel of improved ignitibility from other fuels. Addition ofextraneous ignition-temperature depressants, such as aldehydes, mayresult in the fuel becoming acidic in character duringstorage due tooxygen of the atmosphere slowly reacting with such substances. Toovercome this, I may add to the fuel an oxidation inhibitor such asa-naphthol, and/or other substances, e. g., ammonia or oil-solublebases, which form addition compounds with the aldehydes and thus reducevolatile, preferably petroleum, oil containing selfmadeignition-temperature depressants, an example of such being a nit-ratedvolatile petroleum oil. Certain other aspects of the inventioncontemplate the regulated addition of predetermined proportions ofeXtraneously-formed depressants; especially-oxygenated polyfu-rcoushydrocarbons of the antiknock-igniting type. Still another aspect isthat which involves thegradual and continuous addition of suchdepressants to theiuel as fed to the engine. The compositicnherein thusconstitutes a motor fuel preferably of a volatile character of thegasoline type, preferably neutral and preferably substantiallynon-corrosive which contains an ignition-temperature depressantpreferably of a pressure-activated type, that is, a substance or mixtureof substances which at the compression pressures of the engine becomeadequately responsive to ignition as compared with gasoline of normalignitibility; the improved mothe invention contemplates a motor fuelcomprising a Addition of a. 45

l'il

bility at atmospheric pressure which approximates that of ordinary ornormal gasoline but which under engine compression presents a degree ofignitibility greater in proportion than would correspond to the ease ofignition of the same gasoline untreated or of normal gasoline under likeconditions of compression. 7

The following examples will serve to illustrate I my invention:

Emample 1.-Distil 400 F. end-point gasoline, taking over the fractionboiling up to 175 F. After cooling toatmospheric temperature, add 5volumes of nitric acid of specific gravity 1.05 to 100 volumes of thehigher-boiling fraction. Thoroughly agitate the mixture keeping thetemperature at 70 .5. After agitation let the mixture stand wherebyseparation into two layers takes place. drawn and the upper, or oil,layer iswashed with water and then with a dilute solution of sodiumcarbonate. Addition of the low-boiling fraction to the treatedhigh-boiling fraction gives a nitrated gasoline.

Example 2.To 80 parts of isopropyl alcohol add parts of trioxymethyleneand into this mixture pass some dry gaseous hydrogen chloride. Let themixture stand at atmospheric temperature for. hours. Filter anyundissolved material, neutralize the filtrate with sodium bicarbonateand distil, preserving the fraction boiling between about 90 and 120 C.,which contains a large proportion of diisopropyl formol.

cm H cm I cnoconc Add 20 parts of this fraction to 100 parts of 325 F.end-point gasoline to produce an aviation fuel containing a polyfurcousantiknock-igniter.

Example 3.-Prepare the reaction product of isopropyl alcohol andformaldehyde as described in Example 2. The fraction boiling between 90and 120 C. is washed with water, dried, and added to 400 F. end-pointgasoline in the proportion of volumes of antiknock-igniter to 100volumes of gasoline.

Example 4.Add 10. volumes of cracked isopropyl alcohols, prepared byconducting the vapors of isopropyl alcohol through a copper tube heatedto 600 C., and volumes of diisopropyl formal, prepared as described inExample 2, to 150 volumes of 400 F. end-point straight-run gasolinethereby to obtain a. motor fuel containing both a polyfurcousanti-knock-igniter and an ignition temperature depressant.

Example 5.Add 20 volumes of the acetal, as prepared in Example 2, and 2volumes of acetaldehyde to 100 volumes of 400 end-point gasoline.thereby to obtain a gasoline containing both a polyfurcousantiknock-igniter and an ignition temperature depressant.

Example 6.Add 15 parts of trioxymethylene to 100 parts of tertiary butylalcohol, and then pass in dry hydrogen chloride gas. Proceed as inExample 2, with the exception that the portion distilled above 83 0.,and containing a substantial proportion of di-tertiarybutyl formal,

CH7CO(:JOCCH: 7 OH; H CH3 is preserved. Add 5 volumes of this fractionto 100 volumes of 325 F. end-point gasoline, thus v iving a polyfurcousmotor fuel.

The lower, or acid, layer is with-- tion of Example 1, add diisopropylformal in the ratio of 200 volumes of the nitrated fraction to 5 volumesof the acetal. The low-boiling fraction is united with this mixture togive a nitrated gasoline containing a polyfurcous antiknock-igniter.

Example 8.-Prepare diisobutylene from olefins of cracked gasoline (vaporphase) by suitable polymerization. Pass this dimer, admixed with air,over heated vanadium catalyst to obtain an acid mixture containing alarge proportion of trimethyl-acetic acid. Esterifying this crude acidmixture with isopropyl alcohol to yield a mixture of esters withisopropyl trlmethylacetic ester,

a predominating component. Mix the well-dried crude trimethyl-aceticester with 400 F. endpoint gasoline in the proportion of 92 gallons ofgasoline to 8 gallons of this branchy type of ester.

Example 9.-To provide for top lubrication in the engine, add 1 quart ofa highly refined oil of the gas oil type to 25 gallons of the fuel asprepared according to Example 8.

Example 10.-Prepare cobalt salts of oxidized parafiin wax acids-by theinteraction of a soluble cobalt salt and the sodium salts of the acids.The washed and dried cobalt salts are dissolved in gasoline to give a 1per cent solution. Add one volume of this solution to 100 volumes ofgasoline of Example 8 to furnish a thickened motor fuel.

Example 11.--Prepare a winter gasoline as described in Example 6.Prepare a summer antiknock gasoline by the catalytic hydrogenation ofhigh-boiling petroleum fractions- (i. e., fractions of the gas oil rangeor higher). The summer gasoline is colored by the addition of about0.001 per cent of an oil-soluble recl dye. Summer gasoline and wintergasoline are mixed in the proportion of equal volumes.

Example 12.Dlstil cracked gasoline taking over the fraction boiling upto 320 F. The higher boiling fraction is nitrated as in Example 1. Add20 volumes of this nitrated fraction to 100 volumes of safety fuel, thelatter being obtained by the catalytic hydrogenation of high-boilingpetroleum distillates.

Example 13.-Separate cracked gasoline into two fractions by distillationand nitrate the higherboiling fraction as described in Example 1. To 100volumes of the lower-boiling fraction add 10 volumesof a mixture ofabout equal volumes of ethylene and propylene oxides and 30 volumes ofan antiknock-igniter prepared from secondary butyl alcohol andacetaldehyde. Blend the two fractions thereby obtaining a 400 F.end-point gasoline containing both nitrated ignition-temperaturedepressants and antiknock-igniters.

Example 14.Separate cracked gasoline into two fractions by distillationand treat each fracion separately as described in Example 13. To thehigh-boiling nitrated fraction add about 0.5 per cent by volume of ahighly refined petroleum oil of the gas oil type. To the low-boilingfrac tion, containing the added olefin oxides and antiknock-igniter, isadded about 0.005 per cent of a red oil-soluble dye. The two fractionsare then blended. To the blended gasoline add about 0.1 per cent byweight of a gum-inhibitor, e. g., anaphthol, and about 0.01 per cent byweight of the cobalt salts of wax acids as thickeners.

Example 15.Crack the gas oil fractions, obtained by the distillation ofcrude petroleum, at a temperature of 900 F. and a pressure of 200 poundsper square inch. Pass a portion of the olefin-containing gases fromthiscracking operation through an electric arc to make acetylene.Hydrate separately the acetylene to acetaldehyde and the remainingportion of olefin-containing gas to a mixture of secondary and tertiaryalcohols. Condense the acetaldehyde with the alcohols to obtain amixture of polyfurcous antiknock-igniters.

Example 16.Ma ke an olefin-containing gas as described in Example 15.Pass such a gas through sulphuric acid, absorbing the olefins andleaving a residual gas containing saturated or paraifinic hydrocarbons.Dilute the sulphuric acid solution with water, and distil to obtainalcohols. Conduct the residual gas through an electric arc wherebyacetylene is formed, and hydrate acetylene to acetaldehyde. Condense thealcohols and acetaldehyde to form a mixture of polyfurcousantiknock-igniters.

Example 17.--The uncondensed gases (consisting of paraflin and olefinhydrocarbons having from 1 to carbon atoms per molecule) from thestabilizing unit for cracked gasolines are treated as described inExample 16. The alcohols and acetaldehyde are condensed, in the presenceof hydrogen chloride as a catalyst, to give a mixture of polyfurcousantiknock-igniters.

Example 18.Still gases from the distillation of a petroleum crude oilare subjected to an absorption operation whereby the less volatileconstituents are removed by absorption in a highboiling petroleumfraction. Pass the residual gases, consisting substantially of propaneand butanes, through an electric arc. Hydrate the acetylene formed toacetaldehyde, and condense the acetaldehyde with the alcohols, asprepared in Example 15, to yield polyfurcous antiknock-igniters.

Example 19.--Add 40 volumes or isopropyl trimethyl-acetic ester. asprepared in Example 8, to

volumes of 375 F. end-point gasoline to obtain a racing fuel containingpolyfurcous antiknockigniters.

Example 20.-Prepare a racing fuel of. the polyi'urcousantiknock'-igniti0n type by the addition of 60 volumes of productprepared as in Example 15 to 40 volumes of 375 fiend-point gasoline.

Example 22.Prepare a racing fuel by the addition of volumes of thepclyfurcous antlknock-igniter made by the condensation of secondarybutyl alcohol and acetaldehyde to 20 volumes of 325 F. end-pointgasoline.

Example 21.Prepare a racing fuel by the addition of 80 volumes of thepolyturcous antiknockigniter made by condensation of secondary butylalcohol and acetaldehyde to 20 volumes of 325 F. end-point gasoline.

Example 22.-Prepare ethylene glycol from ethylene of cracking gas ofpetroleum oil cracking. Also by the electric arc treatment of naturalgas, propane, butane, or refinery gas produce.

acetylene and convert this to acetaldehyde. Heat the ethylene glycolwith the acetaldehyde, with or without catalysts, at -160 C. underpressure to form cyclic acetals. Rectify by distillation. Incorporatethis with gasoline in proportions represented by ratios 1:2, 1:3, 1:4,1:7, and the like.

Example 23.--Prcceed as in Example 22 except use formaldehyde.

Example 24.--Use trioxym'ethylene in place of formaldehyde in Example23, in which case heating can be carried out at atmospheric pressure.Diethylene glycol may be used instead of ethylene glycol. I i

In the following claims the word acetal is used in a generic sense toinclude the reaction of the products of aldehydes and alcoholsirrespective of the specific aldehyde used, for example, whetherformaldehyde, acetaldehyde, or other low boiling aldehyde.

What I claim is:

-1. A motor fuel comprising a mixture of light hydrocarbons and anacetal which has at least one bifurcous terminal.

2. A motor fuel according to claim 1 in which the aceta has twobifurcous terminals.

3. A motor fuel comprising gasoline and an addition agent of the typeprepared from the reaction of a low boiling aldehyde and an alcoholselected from the group consisting of secondary and tertiary alcohols.

4. A composition according to claim 3 in which the agent is preparedfrom a secondary alcohol.

5. A composition according to claim 3 in which the agent is preparedfrom isopropyl alcohol.

6. A composition according to claim 3 in which the agent is diisopropylacetal.

'1. A composition according to claim 3 in whic the agent is preparedfrom secondary butyl alcohol.

8. A composition according to claim 3 in which the agent is di-secondarybutyl acetal.

9. A composition according to claim 3 in which the agent is preparedfrom tertiary butyl alcohol.

10. A composition according to claim 3 in which the agent is ditertlarybutyl acetal.

CARLI'I'ON ELLIS.

